An ink composition or a toner composition has been prepared conventionally by dissolving or dispersing a colorant. Various polymer materials have been used preferably therefore, and examples of the polymer materials include a styryl, acryl, or methacrylic polymer compound. A colorant composition containing a solvent or water as a base material generally employs a polymer material preferably having an ionic functional group, as an attempt at improving dispersibility of the colorant such as a pigment.
Meanwhile, a polymer compound having a polyvinyl ether main chain is also known as a polymer material having a flexible polymer chain. However, an ionic functional group is rarely introduced into a repeating unit of the polymer compound. Candidates for the ionic functional group such as carboxylic acids and carboxylate esters are reported, but more stable compounds are actually demanded (see Journal of Polymer Science, Part A, Polymer Chemistry, 27, 3303-3314 (1989)).
An aqueous dispersing material contains a functional substance, and conventionally known examples of the functional material include: pesticides such as a herbicide and an insecticide; pharmaceuticals such as an anticancer agent, an antiallergic drug, and an anti-inflammatory; and colorants each containing a colorant such as an ink and a toner. A digital printing technique has recently progressed at a remarkable rate. Typical examples of the digital printing technique include an electrophotographic technique and an ink jet technique, and the digital printing technique has increasingly enhanced its raison d'etre recently as an image forming technique in an office, home, or the like.
Of those, the ink jet technique has such a remarkable feature that it provides a compact, low-power consumption direct recording method. Further, miniaturization of nozzles or the like has rapidly enhanced image quality. An example of the ink jet technique involves: evaporating and bubbling an ink supplied from an ink tank by heating with a heater in a nozzle; and ejecting the ink, to thereby form an image on a recording medium. Another example thereof involves ejecting an ink from a nozzle by vibrating a piezoelectric element.
The ink used in such methods usually employs an aqueous dye solution, and may result in bleeding when overlapping colors or a phenomenon called feathering in a grain direction of paper at recording positions on the recording medium. Use of a pigment-dispersed ink has been studied for solving such problems (see U.S. Pat. No. 5,085,698). However, much improvement is still desired.